How to bin 2d data?
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Dear all,
I have a 2-dimension coordinate set (x,y) which contains 5000 points and I want to construct a 2d map to reflect the point density distribution. firstly I want to divide both of the ranges of the two coordinate sets (-3 to2 for x; and -2.5 to 3 for y) into like 37 bins,so there will be totally 37x37 bins. Then I want to assign each point into these bins.To do that I need to construct a indicator function δkij (k=1:5000; i=1:37; j=1:37) which denotes whether point k falls in bin (i,j): if point k falls into bin (i,j), then δkij=1, otherwiseδkij=0. Then the histogram at bin (i,j) is the sum of δkij (k=1:5000). At last I wish to plot a contour map or hotmap to show the hisrogram. How does matlab realize these computation?
All the best!
Yeping Sun
댓글 수: 1
Azzi Abdelmalek
2016년 8월 6일
Your question is not clear, post a short example, give a brief explanation on what you want, then post the expected result
채택된 답변
Image Analyst
2016년 8월 6일
편집: Image Analyst
2016년 8월 6일
Try (the badly named) hist3() to construct a 2-D histogram:
% Create sample data.
numPoints = 5000;
x = -3 + 5 * rand(numPoints, 1);
y = -2.5 + 5.5 * rand(numPoints, 1);
% Now construct the histogram
xy = [x, y];
subplot(1,2,1);
hist3(xy, [37, 37]); % Plots bar chart.
subplot(1,2,2);
counts = hist3(xy, [37, 37]);
imshow(counts, []); % Show as image
colormap(hot(256));
colorbar;
axis on;
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/174827/image.png)
댓글 수: 8
Image Analyst
2016년 8월 9일
SOrry, I meant XData and YData, like this:
imshow(heatMap, 'XData', [-3 3], 'YData', [-3,3]);
but you should really use histogram2() and get the BinEdges property and use that instead of [-3, 3] because [-3,3] may not be correct if the histogram was automatic. However if you passed in the edges, then you know what the edges are and you can use that.
추가 답변 (2개)
Steven Lord
2016년 8월 6일
Use the histogram2 function. The DisplayStyle 'tile' looks like it's exactly what you're looking for.
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Thorsten
2016년 8월 9일
편집: Thorsten
2016년 8월 9일
Have a look at this:
D = dlmread('/Users/hansen/Downloads/PC1-PC2.txt');
Nbins = 37;
H = hist3(D, {linspace(-3,3,Nbins) linspace(-3,3,Nbins)});
imshow(H, [])
colormap hot
colorbar
The values of H are in the range [0, 196], and that is the range of the colorbar.
For a contour plot, use:
contour(H)
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